1. Field of the Invention
This invention relates generally to the structure and fabrication process of a Schottky barrier rectifier. More particularly, this invention relates to a novel Schottky device structure and fabrication process where a requirement of p-ring is eliminated and meanwhile the forward current is enhanced and the reverse breakdown voltage is improved.
2. Description of the Prior Art
Conventional rectifier with a Schottky barrier configuration is limited by the technical difficulties of low efficiency, low switching speed, and low reverse breakdown voltage. These difficulties hinders practical applications of the Schottky rectifiers in modern electronic devices when the operational voltage drops from twelve volts to five volts and further down to three volts and lower voltages when the technology moving toward quarter micron feature size and beyond.
FIG. 1 shows a cross sectional view of a conventional Schottky barrier rectifier 10. An N-layer 20 is supported on a N+ substrate 15. In the N-layer 20 a p-ring 25 is formed to eliminate the sharp edge effects between the metal layers 30 and the top surface above the N-layer. The requirement to form the P-ring 25 in the N-layer 20 is to prevent a reverse breakdown due to the sharp edges formed between the metal layer 30 and the top surface of the N-layer 20. However, due to the requirement of providing the p-ring 25, the thickness of the N-layer is limited. The forward voltage V.sub.f and the forward current I.sub.f are limited. Additionally, due to the p-n junction formed between the P-ring 25 and the N-layer 20, the switching speed of the Schottky rectifier is adversely affected.
In U.S. Pat. No. 5,686,753, entitled "Schottky Barrier Diode having a Mesa Structure" Miyata el al. disclose a Schottky barrier diode as that shown in FIG. 2. It includes a compound semiconductor substrate having an N+ layer and an N- layer with the N- layer supported on the N+ layer. The N- layer is configured in a form of a mesa, which has a skirt portion and a slant portion. The diode further includes an insulation layer formed on the skirt portion and the slant portion of the mesa. An anode is formed on the insulation layer and the N- layer. A cathode is formed on the N+ layer. Even with a mesa shape, Miyata's Schottky barrier diode still faced with the problem of sharp edge effect between the anode layer and the N- layer. A reverse breakdown problem would hinder practical application of the device as disclosed in the patent.
Therefore, a need still exits in the art of design and fabrication of the Schottky rectifiers, particularly for low voltage rectifiers, to provide a structure and fabrication process that would resolve these difficulties. More specifically, it is preferably that a Schottky rectifier with a high efficiency can be produced with effective prevention against reverse breakdown without causing a slow down of the switching speed. It is further desirable to employ a simplified manufacture process to reduce the production costs such that a high quality high performance Schottky rectifier can be economically applied.